The present disclosure relates to inkjet recording apparatuses for performing recording by ejecting ink onto a recording medium, such as paper, and in particular to recovery of a recording head used to eject ink.
Recording apparatuses, such as facsimile machines, copiers, and printers, are structured to record images onto a recording medium, such as paper, cloth, or an overhead projector film, for example. Such recording apparatuses can be classified into an inkjet type, a wire dot type, and a thermal type according to the method employed for the recording. The inkjet recording method can further be classified into a serial head type and a line head type. A recording apparatus of the serial head type performs recording while moving the recording head across the recording medium. A recording apparatus of the line head type performs recording with the recording head fixed to the main body.
A recording apparatus of the inkjet type includes a plurality of nozzles each for ejecting ink. Unfortunately, in a nozzle that is placed standby or not used for printing, ink may thicken and thus the linearity of ink ejection may decrease (trajectory deflection) or failure of ink ejection may occur. In addition, trajectory deflection of the ejected ink may occur at the time of successive print operations. Trajectory deflection may result in image quality degradation or contamination by the ink within the apparatus. The cause of such trajectory deflection has been clarified to be meniscus abnormality. For example, meniscus abnormality may be caused by dispersion particles or surfactant components adhered to or precipitated in the nozzle. Meniscus abnormality may also be caused by ink mists or foreign matter (paper dust or the like) adhered to the nozzle.
Piezoelectric inkjet heads are widely used as the recording heads for inkjet recording apparatuses. A piezoelectric inkjet head deforms a piezoelectric element to apply pressure to the ink in a pressure chamber, which then causes the ink meniscus in the nozzle to oscillate so that ink droplets are ejected.
The piezoelectric inkjet head may change the size of ink droplets to be ejected so as to reproduce gradation within one image. To this end, pulses of the drive waveform applied to cause ejection of ink droplets are changed to control oscillation of the meniscus. However, the meniscus is instable due to the presence of the incoming flow of ink into the pressure chamber (inertance), which may impair the linearity of the trajectory of ejected ink.
In view of the above, various methods have been suggested to suppress occurrence of meniscus abnormality.
For example, in one method suggested, occurrence of meniscus abnormality is suppressed by devising the nozzle shape. More specifically, providing a projection on an edge of the nozzle is suggested in the method. In another method suggested, the peripheral edge of a nozzle is projected from the nozzle plate so as to cause the meniscus of ink to be formed at the end face of the nozzle orifice.
In a yet another method suggested, the inner wall of a nozzle is treated to impart ink-repellency and ink-affinity to improve the surface property of the nozzle.
In a yet another method suggested, a cleaning fluid is supplied to the nozzle surface and the nozzle surface is cleaned with a brush.
In a yet another method suggested, the angle formed between the meniscus edge and the nozzle plate is made larger at the time of ejection driving for idle striking to recover the ejection function of the nozzle than at the time of ejection driving for actually ejecting ink to form images. As a result, foreign matter residing near the nozzle plate is integrated into ink droplets and removed at the time of practice ejection.